Rough idle after Pre-cat removal

daiflu

Hey guys, removed my pre-cat last night.
I took it for a test drive today and noticed two problem;
Usual running temp is up 5deg or so and the idle is now a little lower (600rpm) and is quite rough, sound as if it's about to stall.
Any ideas guys? Anyone else have this problem?
I did a search and found a few have complained about low/rough idle, however not directly after pre-cat removal.

JohnnyN

Did you disconnect the battery for 30 minutes? If not, disconnect the battery as I have mentioned for 30 minutes. After reconnecting, drive the car steadily for 50 miles trying not to rev over 3500rpm. This should give the ECU time to adjust.

;-)

daiflu

Nope.
I'll go whip it off now.
Thanks mate!

adie2_2

Why specificly under 3500 rpm ? iask as I disconnected my battery the other day after swapping my TB over, my eml come on and I didnt run it as such under 3500rpm, I have found no differance dunno.. [/quote]

JohnnyN

Its been found that by running the car steadily the ECU learns a smooth set of fuelling parameters. Vocky can advise further on this.

daiflu

OK, just got back from an 80km drive up and down my nearest freeway.
🙁 No luck. Still running slightly hotter, rough idle (it's like it's just on the low side 50-100rpm). Engine feels restricted somewhat and seems to have worse throttle response.
It's also very hard to start.
All i can think of is something to do with one of the Lambda sensors. I was reasonably careful with these, but when removing them, the wires were twisted (caused by un-screwing the sensor) and then again when re-installing.Is there a way to check that they are functioning properly?
How to i put them back and ensure the wires are not twisted, like the factory install?
Can I unplug them from the other end and un-twist them?

l1ghtn1ng

Just a thought but did any material from the precat you drilled out drop down the pipe to the maincat? If so it could of caused the cat to block up

DBcoup

l1ghtn1ng said:
Just a thought but did any material from the precat you drilled out drop down the pipe to the maincat? If so it could of caused the cat to block up

I was thinking exactly the same :?

daiflu

It's certainly possible. The core of the cat came out as mostly one chunk, but when drilling/chiselling into it there would be debris around the sides. I did turn it up and tap it intermittently, and again at the end though.
Is there any way of knowing for sure? And if so, getting it out? I don’t see much point in taking it out again and trying to get the debris out, as if it was going to come out, it would have when I did it before re-fitting.

daiflu

JohnnyN said:
DO NOT USE WD-40 ON THE SENSORS when removing them!! Can't stress that enough! It ruins them.

This could be my problem. Didn't soaked them, but used it on the thread.
So I'm up for 2 new sensors then?
If the rear sensor is stuffed, will it actually affect the running of the car, or just give a warning light (which I can live with)

vocky

I used wd40 only on the threads...........two new lambda sensors later :roll:

daiflu

Were your symptoms the same Vocky?
Will I need to replace the rear sensor, as in will it actually affect the performance of the engine?
I ask, because I'm looking at installing a Performance cat and O2sim in the near future.

vocky

mine was giving an eml, after replacing the mixture sensor it went much better 🙂

I would try the mixture lambda first, that controls the fuelling, the other lambda only checks the cat is working

daiflu

Ordered a mixture oxygen sensor today from autovaux, so I'll have to wait a few days.
Price from Autovaux = $150AUD delivered called my local Holden dealer = $418AUD!
At that price, I think I'll wait.

Strange thing happened today though, Jupped in the car, started it and she Idled as normal. Thought 'sweet she's fixed herself!' next time I stopped, old lumpy bumpy idle was back 🙁
Then a little later, back to normal! Then back to crap 🙁

Also, has anyone tried cleaning the oxygen sensor using electrical contact cleaner? Read mixed reports, with some swearing it works. Brought a can today, so might give it a go when my new sensor gets here.

daiflu

Ok, my new oxygen sensor showed up, so I thought I would clean the old one and see what happened. I sprayed it using electrical contact cleaner and put it back in.
Started her up, and it was still a little rough. Then I took it for a drive, and to my surprise it actually seemed to come right.
This was a couple of days ago, and now it's back to normal! I can finally feel what it's like with the pre-cat removed!
I will still instal the new sensor since I have it now, but next time your oxygen sensor goes, you might want to try giving it a clean before forking out for a new one.
Of course it could have nothing to do with the clean, as it was improving slightly over time dunno..
All I know is that she's back!!

Now I'm paraniod about the chain after reading the horror stories on this site :roll:

vocky

glad you found the problem 🙂

Lightning_Coupe

Cool, Contact cleaner is one to remember for the future. Has the temperature come back down again now? Is should be lower than before with the pre cat removed. One of the reasons the precat was deleted from manufacture was to reduce the heat build up in the manifold I think, and that should lower the engine temp if anything I'd have thought.

daiflu

yep, temps are back to normal.